A lithography apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs).
In the semiconductor industry there is a strong pressure to increase the density of devices, e.g. transistors, in an integrated circuit that is formed on a substrate. To achieve increased densities, the accuracy and precision of lithography apparatuses and processes must be improved. Amongst other things, it is therefore desirable to improve the accuracy and stability of temperature control within a lithography apparatus or an inspection tool.
Within a lithography apparatus there are various modules which generate heat loads, referred to herein as active modules. Some active modules generate heat loads that are highly variable with time, for example are intermittent. A temperature control system in a lithography apparatus may operate by circulating a thermal transfer fluid, e.g. water, through a conduit close to or in a component whose temperature is to be controlled. The component whose temperature is to be controlled may or may not be part of an active module. The temperature of the thermal transfer fluid is accurately controlled by a temperature control device, e.g. including a heater or a cooler.
If a tight specification for the size and duration of a deviation from the target temperature is set, then the temperature control system has to be capable of removing heat from the vicinity of a an active module at a rate approximately equal to the peak heat load of the active module. For a given thermal transfer fluid, the mass flow rate required to achieve a desired rate of heat removal is determined by the specific heat capacity of the thermal transfer fluid. Even using water as the thermal transfer fluid—since water has a high specific heat capacity—the large number of active modules in a lithographic apparatus means that the total required mass flow rate of the thermal transfer fluid is high.